/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package javax.servlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Locale;

/**
 * Defines an object to assist a servlet in sending a response to the client. The servlet container
 * creates a <code>ServletResponse</code> object and passes it as an argument to the servlet's
 * <code>service</code> method.
 * <p>
 * To send binary data in a MIME body response, use the {@link ServletOutputStream} returned by
 * {@link #getOutputStream}. To send character data, use the <code>PrintWriter</code> object
 * returned by {@link #getWriter}. To mix binary and text data, for example, to create a multipart
 * response, use a <code>ServletOutputStream</code> and manage the character sections manually.
 * <p>
 * The charset for the MIME body response can be specified explicitly using the {@link
 * #setCharacterEncoding} and {@link #setContentType} methods, or implicitly using the {@link
 * #setLocale} method. Explicit specifications take precedence over implicit specifications. If no
 * charset is specified, ISO-8859-1 will be used. The <code>setCharacterEncoding</code>,
 * <code>setContentType</code>, or <code>setLocale</code> method must be called
 * before <code>getWriter</code> and before committing the response for the character encoding to be
 * used.
 * <p>
 * See the Internet RFCs such as <a href="http://www.ietf.org/rfc/rfc2045.txt"> RFC 2045</a> for
 * more information on MIME. Protocols such as SMTP and HTTP define profiles of MIME, and those
 * standards are still evolving.
 *
 * @see ServletOutputStream
 */
public interface ServletResponse {

    /**
     * Returns the name of the character encoding (MIME charset) used for the body sent in this
     * response. The character encoding may have been specified explicitly using the {@link
     * #setCharacterEncoding} or {@link #setContentType} methods, or implicitly using the {@link
     * #setLocale} method. Explicit specifications take precedence over implicit specifications. Calls
     * made to these methods after
     * <code>getWriter</code> has been called or after the response has been
     * committed have no effect on the character encoding. If no character encoding has been
     * specified, <code>ISO-8859-1</code> is returned.
     * <p>
     * See RFC 2047 (http://www.ietf.org/rfc/rfc2047.txt) for more information about character
     * encoding and MIME.
     *
     * @return a <code>String</code> specifying the name of the character encoding, for example,
     * <code>UTF-8</code>
     */
    public String getCharacterEncoding();

    /**
     * Returns the content type used for the MIME body sent in this response. The content type proper
     * must have been specified using {@link #setContentType} before the response is committed. If no
     * content type has been specified, this method returns null. If a content type has been specified
     * and a character encoding has been explicitly or implicitly specified as described in {@link
     * #getCharacterEncoding}, the charset parameter is included in the string returned. If no
     * character encoding has been specified, the charset parameter is omitted.
     *
     * @return a <code>String</code> specifying the content type, for example,
     * <code>text/html; charset=UTF-8</code>, or null
     * @since 2.4
     */
    public String getContentType();

    /**
     * Returns a {@link ServletOutputStream} suitable for writing binary data in the response. The
     * servlet container does not encode the binary data.
     * <p>
     * Calling flush() on the ServletOutputStream commits the response. Either this method or {@link
     * #getWriter} may be called to write the body, not both.
     *
     * @return a {@link ServletOutputStream} for writing binary data
     * @throws IllegalStateException if the <code>getWriter</code> method has been called on this
     * response
     * @throws IOException if an input or output exception occurred
     * @see #getWriter
     */
    public ServletOutputStream getOutputStream() throws IOException;

    /**
     * Returns a <code>PrintWriter</code> object that can send character text to the client. The
     * <code>PrintWriter</code> uses the character encoding returned by {@link #getCharacterEncoding}.
     * If the response's character encoding has not been specified as described in
     * <code>getCharacterEncoding</code> (i.e., the method just returns the
     * default value <code>ISO-8859-1</code>), <code>getWriter</code> updates it to
     * <code>ISO-8859-1</code>.
     * <p>
     * Calling flush() on the <code>PrintWriter</code> commits the response.
     * <p>
     * Either this method or {@link #getOutputStream} may be called to write the body, not both.
     *
     * @return a <code>PrintWriter</code> object that can return character data to the client
     * @throws java.io.UnsupportedEncodingException if the character encoding returned by
     * <code>getCharacterEncoding</code> cannot be used
     * @throws IllegalStateException if the <code>getOutputStream</code> method has already been
     * called for this response object
     * @throws IOException if an input or output exception occurred
     * @see #getOutputStream
     * @see #setCharacterEncoding
     */
    public PrintWriter getWriter() throws IOException;

    /**
     * Sets the character encoding (MIME charset) of the response being sent to the client, for
     * example, to UTF-8. If the character encoding has already been set by {@link #setContentType} or
     * {@link #setLocale}, this method overrides it. Calling {@link #setContentType} with the
     * <code>String</code> of <code>text/html</code> and calling this method
     * with the <code>String</code> of <code>UTF-8</code> is equivalent with calling
     * <code>setContentType</code> with the <code>String</code> of
     * <code>text/html; charset=UTF-8</code>.
     * <p>
     * This method can be called repeatedly to change the character encoding. This method has no
     * effect if it is called after <code>getWriter</code> has been called or after the response has
     * been committed.
     * <p>
     * Containers must communicate the character encoding used for the servlet response's writer to
     * the client if the protocol provides a way for doing so. In the case of HTTP, the character
     * encoding is communicated as part of the <code>Content-Type</code> header for text media types.
     * Note that the character encoding cannot be communicated via HTTP headers if the servlet does
     * not specify a content type; however, it is still used to encode text written via the servlet
     * response's writer.
     *
     * @param charset a String specifying only the character set defined by IANA Character Sets
     * (http://www.iana.org/assignments/character-sets)
     * @see #setContentType #setLocale
     * @since 2.4
     */
    public void setCharacterEncoding(String charset);

    /**
     * Sets the length of the content body in the response In HTTP servlets, this method sets the HTTP
     * Content-Length header.
     *
     * @param len an integer specifying the length of the content being returned to the client; sets
     * the Content-Length header
     */
    public void setContentLength(int len);

    /**
     * Sets the length of the content body in the response In HTTP servlets, this method sets the HTTP
     * Content-Length header.
     *
     * @param length an integer specifying the length of the content being returned to the client;
     * sets the Content-Length header
     * @since Servlet 3.1
     */
    public void setContentLengthLong(long length);

    /**
     * Sets the content type of the response being sent to the client, if the response has not been
     * committed yet. The given content type may include a character encoding specification, for
     * example,
     * <code>text/html;charset=UTF-8</code>. The response's character encoding
     * is only set from the given content type if this method is called before
     * <code>getWriter</code> is called.
     * <p>
     * This method may be called repeatedly to change content type and character encoding. This method
     * has no effect if called after the response has been committed. It does not set the response's
     * character encoding if it is called after <code>getWriter</code> has been called or after the
     * response has been committed.
     * <p>
     * Containers must communicate the content type and the character encoding used for the servlet
     * response's writer to the client if the protocol provides a way for doing so. In the case of
     * HTTP, the
     * <code>Content-Type</code> header is used.
     *
     * @param type a <code>String</code> specifying the MIME type of the content
     * @see #setLocale
     * @see #setCharacterEncoding
     * @see #getOutputStream
     * @see #getWriter
     */
    public void setContentType(String type);

    /**
     * Sets the preferred buffer size for the body of the response. The servlet container will use a
     * buffer at least as large as the size requested. The actual buffer size used can be found using
     * <code>getBufferSize</code>.
     * <p>
     * A larger buffer allows more content to be written before anything is actually sent, thus
     * providing the servlet with more time to set appropriate status codes and headers. A smaller
     * buffer decreases server memory load and allows the client to start receiving data more
     * quickly.
     * <p>
     * This method must be called before any response body content is written; if content has been
     * written or the response object has been committed, this method throws an
     * <code>IllegalStateException</code>.
     *
     * @param size the preferred buffer size
     * @throws IllegalStateException if this method is called after content has been written
     * @see #getBufferSize
     * @see #flushBuffer
     * @see #isCommitted
     * @see #reset
     */
    public void setBufferSize(int size);

    /**
     * Returns the actual buffer size used for the response. If no buffering is used, this method
     * returns 0.
     *
     * @return the actual buffer size used
     * @see #setBufferSize
     * @see #flushBuffer
     * @see #isCommitted
     * @see #reset
     */
    public int getBufferSize();

    /**
     * Forces any content in the buffer to be written to the client. A call to this method
     * automatically commits the response, meaning the status code and headers will be written.
     *
     * @throws IOException if an I/O occurs during the flushing of the response
     * @see #setBufferSize
     * @see #getBufferSize
     * @see #isCommitted
     * @see #reset
     */
    public void flushBuffer() throws IOException;

    /**
     * Clears the content of the underlying buffer in the response without clearing headers or status
     * code. If the response has been committed, this method throws an <code>IllegalStateException</code>.
     *
     * @see #setBufferSize
     * @see #getBufferSize
     * @see #isCommitted
     * @see #reset
     * @since 2.3
     */
    public void resetBuffer();

    /**
     * Returns a boolean indicating if the response has been committed. A committed response has
     * already had its status code and headers written.
     *
     * @return a boolean indicating if the response has been committed
     * @see #setBufferSize
     * @see #getBufferSize
     * @see #flushBuffer
     * @see #reset
     */
    public boolean isCommitted();

    /**
     * Clears any data that exists in the buffer as well as the status code and headers. If the
     * response has been committed, this method throws an
     * <code>IllegalStateException</code>.
     *
     * @throws IllegalStateException if the response has already been committed
     * @see #setBufferSize
     * @see #getBufferSize
     * @see #flushBuffer
     * @see #isCommitted
     */
    public void reset();

    /**
     * Sets the locale of the response, if the response has not been committed yet. It also sets the
     * response's character encoding appropriately for the locale, if the character encoding has not
     * been explicitly set using {@link #setContentType} or {@link #setCharacterEncoding},
     * <code>getWriter</code> hasn't been called yet, and the response hasn't
     * been committed yet. If the deployment descriptor contains a
     * <code>locale-encoding-mapping-list</code> element, and that element
     * provides a mapping for the given locale, that mapping is used. Otherwise, the mapping from
     * locale to character encoding is container dependent.
     * <p>
     * This method may be called repeatedly to change locale and character encoding. The method has no
     * effect if called after the response has been committed. It does not set the response's
     * character encoding if it is called after {@link #setContentType} has been called with a charset
     * specification, after {@link #setCharacterEncoding} has been called, after
     * <code>getWriter</code> has been called, or after the response has been
     * committed.
     * <p>
     * Containers must communicate the locale and the character encoding used for the servlet
     * response's writer to the client if the protocol provides a way for doing so. In the case of
     * HTTP, the locale is communicated via the <code>Content-Language</code> header, the character
     * encoding as part of the <code>Content-Type</code> header for text media types. Note that the
     * character encoding cannot be communicated via HTTP headers if the servlet does not specify a
     * content type; however, it is still used to encode text written via the servlet response's
     * writer.
     *
     * @param loc the locale of the response
     * @see #getLocale
     * @see #setContentType
     * @see #setCharacterEncoding
     */
    public void setLocale(Locale loc);

    /**
     * Returns the locale specified for this response using the {@link #setLocale} method. Calls made
     * to <code>setLocale</code> after the response is committed have no effect.
     *
     * @return The locale specified for this response using the {@link #setLocale} method. If no
     * locale has been specified, the container's default locale is returned.
     * @see #setLocale
     */
    public Locale getLocale();

}
